POPULATION ESTIMATES FOR HUMPBACK CHUB (GILA CYPHA) AND ROUNDTAIL

State of Utah DEPARTMENT OF NATURAL RESOURCES Division of Wildlife Resources – Native Aquatics

POPULATION ESTIMATES FOR HUMPBACK CHUB (GILA CYPHA) AND ROUNDTAIL CHUB (GILA ROBUSTA) IN WESTWATER CANYON,

COLORADO RIVER, UTAH, 1998–2000

Publication Number 03-51 Utah Division of Wildlife Resources

1594 W. North Temple Salt Lake City, Utah

Kevin Conway, Director

Population Estimates for Humpback Chub (Gila cypha) and Roundtail Chub (Gila robusta) in Westwater Canyon,

Colorado River, Utah, 1998–2000

J. Michael Hudson

and

Julie A. Jackson

Utah Division of Wildlife Resources-Moab Field Station 1165 S. Hwy 191-Suite 4

Moab, UT 84532

Final Report December 2003

Upper Colorado River Endangered Fish

Recovery Program Project #22c

Publication Number 03-51 Utah Division of Wildlife Resources

1594 W. North Temple Salt Lake City, Utah

Kevin Conway, Director

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ACKNOWLEDGEMENTS We would like to acknowledge Tom Chart, Melissa Trammel, Steve Meismer, and Pete Cavalli, who leant their considerable biological expertise to various portions of this study. We would also like to thank Dr. Ron Ryel, Utah State University, and Dr. Kevin Bestgen, Colorado State University, for statistical guidance. Many thanks to Dr. Kevin Bestgen, Chuck McAda, and Dr. Rich Valdez for their in depth review and critique of this report. Finally, we would like to thank the numerous technicians and volunteers without whom this study would not have been possible. This study was funded by the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin. The Recovery Program is a joint effort of the U.S. Fish and Wildlife Service, U.S. Bureau of Reclamation, Western Area Power Administration, state of Colorado, Utah, and Wyoming, Upper Basin water users, environmental organizations, the Colorado River Energy Distributors Association, and the National Park Service. Mention of trade names or commercial products does not constitute endorsement of recommendation for use by the authors, the Fish and Wildlife Service, U.S. Department of the Interior, or members of the Recovery Implementation Program.

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TABLE OF CONTENTS ACKNOWLEDGEMENTS ......................................................................................................... ii TABLE OF CONTENTS ............................................................................................................ iii LIST OF TABLES .........................................................................................................................v LIST OF FIGURES .................................................................................................................... vi LIST OF KEY WORDS ............................................................................................................. vii EXECUTIVE SUMMARY ....................................................................................................... viii INTRODUCTION..........................................................................................................................1 METHODS .....................................................................................................................................2 Study Area ...........................................................................................................................2 Sampling..............................................................................................................................2 Data Analysis.......................................................................................................................3 Population Estimate.................................................................................................3 CPUE .......................................................................................................................3 Length-Frequency ....................................................................................................4 Growth .....................................................................................................................4 Movement .................................................................................................................4 Comparison with ISMP............................................................................................4 RESULTS .......................................................................................................................................4 Humpback Chub .................................................................................................................4 Population Estimates ...............................................................................................4 CPUE .......................................................................................................................5 Length-Frequency ....................................................................................................5 Growth .....................................................................................................................6 Movement .................................................................................................................6 Comparison with ISMP............................................................................................6 Roundtail Chub ...................................................................................................................7 Population Estimates ...............................................................................................7 CPUE .......................................................................................................................7 Length-Frequency ....................................................................................................8 Growth .....................................................................................................................8 Movement .................................................................................................................8 Comparison with ISMP............................................................................................8

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TABLE OF CONTENTS (continued) DISCUSSION .................................................................................................................................9 Population Estimates ..........................................................................................................9 Length-Frequency.............................................................................................................10 Growth ...............................................................................................................................10 Movement ..........................................................................................................................11 Comparison with ISMP ....................................................................................................12 CONCLUSIONS ..........................................................................................................................13 RECOMMENDATIONS.............................................................................................................14 LITERATURE CITED ...............................................................................................................15 APPENDICES ..............................................................................................................................29

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LIST OF TABLES Table 1. Population estimate for humpback chub adults in Westwater Canyon 1998–2000..............................................................................................................17 Table 2. Total humpback chub captures in Westwater Canyon 1998–2000........................17 Table 3. Population estimate for roundtail chub adults in Westwater Canyon 1998–2000..............................................................................................................18 Table 4. Total roundtail chub captures in Westwater Canyon 1998–2000..........................18 Appendix I. Summary of population estimates generated within Program CAPTURE for adult humpback chub in Westwater Canyon, 1998–2000 .....................................29 Appendix II. Summary of population estimates generated within Program CAPTURE for adult roundtail chub in Westwater Canyon, 1998–2000........................................30

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LIST OF FIGURES Figure 1. Westwater Canyon adult humpback chub population estimates for 1998–2000..............................................................................................................19 Figure 2. Westwater Canyon humpback chub trammel net catch per unit effort by pass for 1998–2000 ................................................................................................19 Figure 3. Westwater Canyon humpback chub length-frequency histograms for 1998– 2000........................................................................................................................20 Figure 4. Westwater Canyon humpback chub annual incremental growth for individuals between 1998–1999 and 1999–2000, and among all years.................21 Figure 5. Westwater Canyon humpback chub catch per unit effort for samples collected using ISMP protocol from 1988 to 2000................................................21 Figure 6. Westwater Canyon humpback chub ISMP length-frequency histograms for 1988–2000........................................................................................................22 Figure 7. Westwater Canyon adult roundtail chub population estimates for 1998–2000..............................................................................................................24 Figure 8. Westwater Canyon roundtail chub trammel net catch per unit effort by pass for 1998–2000 ................................................................................................24 Figure 9. Westwater Canyon roundtail chub length-frequency histograms for 1998– 2000........................................................................................................................25 Figure 10. Westwater Canyon roundtail chub annual incremental growth for individuals between 1998–1999 and 1999–2000, and among all years.................26 Figure 11. Westwater Canyon roundtail chub catch per unit effort for samples collected using ISMP protocol from 1988 to 2000................................................26 Figure 12. Westwater Canyon roundtail chub ISMP length-frequency histograms for 1988–2000........................................................................................................27

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LIST OF KEY WORDS humpback chub, Gila cypha, roundtail chub, Gila robusta, Westwater Canyon, Colorado River, population estimate, growth, movement

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EXECUTIVE SUMMARY Humpback chub (Gila cypha) are listed under the Endangered Species Act of 1973, as amended. In accordance with recovery goals finalized in 2002, a population estimate was completed for adult humpback chub in Westwater Canyon on the Colorado River. This population estimate was conducted from 1998 to 2000 with the objectives of obtaining population estimates for humpback chub and roundtail chub in Westwater Canyon. Sampling occurred during September and October throughout the three years of the study. Three passes were conducted annually with approximately one week between passes. The primary method of capture was via trammel netting with supplemental electrofishing on one pass per year. Population estimates were generated from recapture data using the null estimator (Mo) within Program CAPTURE. Separate estimates were generated for each year of the study. Results indicated a decline in the adult humpback chub population between 1998-1999 with a retention in abundance between 1999-2000: 4,744 in 1998; 2,215 in 1999; and 2,201 in 2000. This overall declining trend was not statistically significant, but may be of concern. The adult roundtail chub population in Westwater Canyon during this time period was relatively stable: 5,005 in 1998; 4,234 in 1999; and 4,971 in 2000. Length-frequency analysis for both species indicated shifts in the size class structure through the three years. Growth of humpback chub was slower than roundtail chub based on recapture data from this and previous studies. Analysis of recaptures indicated more net movement from humpback chub than from roundtail chub. However, both species exhibited movement between Black Rocks and Westwater Canyon. This movement was frequent enough to consider Black Rocks and Westwater Canyon a single population for humpback chub and roundtail chub. Analysis of catch per unit effort (CPUE) data from this study and historic interagency standardized monitoring indicated a continued declining trend in mean CPUE for humpback chub that was significant. Mean CPUE for roundtail chub also indicated a continued declining trend, but it was not statistically significant. The results of this study will provide valuable information for conducting future population estimates of chub in the upper Colorado River basin in addition to providing three point estimates that will be used to determine if humpback chub have met the recovery goals.

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INTRODUCTION The humpback chub (Gila cypha) was first described in 1945 (Miller 1946). Due to declines in distribution and abundance throughout its range, the humpback chub is currently protected under the Endangered Species Act of 1973, as amended (ESA, 16 U.S.C. 1531 et. seq.). Previously, it was protected under the Endangered Species Conservation Act of 1969 (16 U.S.C. 668aa). The most recent recovery plan was finalized in 1990 (USFWS 1990), with an amendment and supplement to that plan approved in 2002 (USFWS 2002). The amendment and supplement to the 1990 recovery plan identifies objective, measurable recovery criteria to downlist and delist humpback chub in both the upper basin recovery unit and the lower basin recovery unit. Within the upper basin recovery unit, one of the criteria to downlist humpback chub is the maintenance of one of the five upper basin populations (Black Rocks, Westwater Canyon, Cataract Canyon, Yampa Canyon, Desolation/Gray Canyon) as a core population with a minimum viable population of 2,100 adults (≥ 200 mm) for five consecutive years. To delist humpback chub, the upper basin recovery unit will have to maintain this minimum viable population for an additional three years in two of the five upper basin humpback chub populations. The adult humpback chub population will be determined via point estimates in 2–3 of every five years to measure progress toward achieving and maintaining the minimum viable population. Within each core population, there must not be a significant decline of the trend in adult point estimates to downlist and delist humpback chub. The Westwater Canyon adult humpback chub population estimate, along with the Black Rocks humpback chub population estimate, is one of the first upper basin population estimates to be conducted in accordance with these recovery goals. This study was conducted from 1998 to 2000 with the objective of obtaining a population estimate of adult humpback chub in Westwater Canyon. A secondary objective was to obtain a population estimate for roundtail chub (Gila robusta) in Westwater Canyon. Previous efforts (e.g., Chart and Lentsch 1999) to estimate the adult humpback chub population in this canyon had been relatively unsuccessful due to a sampling approach that was not designed to obtain a population estimate. Recommendations from that report included the need to initiate a specific study to generate population estimates in Westwater Canyon with a more aggressive sampling program and a more rigid study design. The result was the current study design. This study was initiated with the understanding that modifications would be made to the approach as more information was gained toward obtaining the most accurate and precise population estimate for adult humpback chub in Westwater Canyon. The results of this study will provide valuable information for conducting future population estimates of chub in the upper Colorado River basin in addition to providing three point estimates that will aid in reclassification of humpback chub under ESA (i.e., downlist, delist).

The objectives of this study are: • To obtain a population estimate of adult humpback chub (≥ 200 mm) in Westwater Canyon. • To obtain a population estimate of adult roundtail chub (≥ 200 mm) in Westwater Canyon. These objectives are specific to Task 4 of the Upper Colorado River Endangered Fish Recovery Program Project 22c – Interagency Standardized Monitoring Program – Utah. This task was added

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to a much larger ongoing project encompassing the entire Colorado River basin in Utah that included many additional objectives. These additional objectives are not addressed in this report.

METHODS Study Area Westwater Canyon is located on the Colorado River downstream of the CO-UT border. The length of the canyon extends approximately twelve miles (RM 124.5–112.5). It is characterized by the black Proterozoic gneiss and granite complex that comprise the inner gorge. The habitat in the upper section of the canyon consists of runs, eddies, and pools interspersed between riffles and rapids. The steepest part of Westwater Canyon is the middle section (RM 119.5–116.5). This portion of the canyon was not sampled due to the turbulent flows and Class III rapids. However, U.S. Fish and Wildlife Service sampled the middle section of Westwater Canyon during 1979-1981 and humpback chub were present (Valdez et al. 1982). The lower section of Westwater Canyon is a confined canyon reach with a reduced gradient that primarily comprises a homogeneous run where chubs are scarce (Chart and Lentsch 1999). Humpback chub sampling occurred at three sites in the upper portion of Westwater Canyon previously established for the Interagency Standardized Monitoring Program (ISMP): Miners Cabin (RM 124.1–123.8), Cougar Bar (RM 121.5–121.0), and Hades Bar (RM 120.0–119.8). Depth measurements collected in 1994 for each of these sites resulted in maximum depths of 21.8 m at Miners Cabin, 19.5 m at Cougar Bar, and 10.6 m at Hades Bar (Chart and Lentsch 1999). Each of these deep canyon habitats is bounded by a riffle area. Sampling Humpback chub sampling in Westwater Canyon occurred during September and October throughout the three years of the study. Three sampling passes were conducted each year. Eight days lapsed between the end of one pass and the beginning of the subsequent pass. During each pass, Miners Cabin was sampled for two nights, Cougar Bar was sampled for two nights and Hades Bar was sampled for one night. Gear included the use of trammel nets (23 m x 2 m; 2.5 cm and 1.25 cm mesh) and a pulsed DC Coffelt® electrofishing unit mounted on an inflatable sport boat. Trammel nets were set in mid-afternoon and checked every two hours until midnight, at which time they were pulled. Nets were reset before dawn and allowed to fish until late morning while being checked every two hours. Trammel nets were set to target juvenile and adult chubs. Trammel nets were primarily set in deep eddies off boulders or rock faces. Nets were occasionally set in relatively shallow riffle/run areas off in-channel boulders. All Gila spp. caught were removed from the net and placed in a holding pen until they were processed at the end of each 18-hour sampling period. Electrofishing was conducted at each site during a single pass each year to continue the protocol established with ISMP (USFWS 1987). Shoreline habitats were electrofished within each site. Electrofishing efforts occurred prior to nets being set in late afternoon and subsequent to nets being pulled at night during each 18-hour sampling period. Electrofishing was conducted to monitor the fish community of Westwater Canyon and to target smaller Gila spp. in addition to the late

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juvenile/adult component of the population. Electrofishing data was specifically used for initial captures in the population estimate, length-frequency analysis and determining movement of Gila in Westwater Canyon. Gila were identified to species using a suite of diagnostic characters (i.e., degree of frontal depression, presence of scales on nuchal hump, “angle of the dangle”, etc.) in conjunction with the “art of seeing well” (Douglas et al. 1998). Information collected from all Gila spp. captures included total length (mm), weight (g), sex (mature chubs; 1998 and 2000), and dorsal and anal fin ray counts. In addition, PIT tag numbers were recorded from recaptured chubs. Initial chub captures of fish greater than 150 mm received a PIT tag and the number was recorded. Information collected for all fish species caught included total and standard lengths (mm) and weight (g). Information collected for other endangered species captured included total and length (mm), weight (g), and PIT tag number. Data Analysis Population Estimate Population estimates were determined for adult humpback chub and roundtail chub (>200 mm) in Westwater Canyon using closed population models within Program CAPTURE (Otis et al. 1978, White et al. 1982, Rexstad and Burnham 1991). Program CAPTURE was used for model selection to help determine the most appropriate estimator but population estimates were routinely calculated using several estimators (Appendices I–II): Mo (null estimator), Jackknife Mh, Darroch Mt, Chao Mth, Chao Mt, and Chao Mh. A separate adult population estimate was calculated for each species in each year. Program CAPTURE was used to determine confidence intervals around the estimate, the coeffiecient of variation, and the probability of capture. Linear regression analyses were conducted on the resulting population estimates for the respective species to examine short-term trends in the populations throughout the period of this study. Confidence intervals were determined for all estimators. Profile likelihood intervals are provided in lieu of 95% confidence intervals for Mo (null estimator) and the Darroch Mt. The profile likelihood interval helps to account for model selection uncertainty by providing wider confidence intervals (Appendix I; David R. Anderson and Gary C. White, Colorado State University, Ft. Collins, Colorado personal communication). In addition, these intervals tend to give more correct confidence intervals for small samples (Ross Moore, Mathematics Department, Macquarie University, Sydney, Australia personal communication). All confidence intervals are provided for comparison among all estimators used to calculate population estimates in Westwater Canyon (Appendices I–II). CPUE Catch per unit effort (CPUE) was determined for trammel net effort toward the capture of humpback chub and roundtail chub through the period of this study. CPUE was compared between passes within and among years using the Kruskal-Wallis nonparametric ANOVA with Dunn’s multiple comparisons test to examine the equality of samples and the two-sample Kolmogorov-Smirnov to compare the distribution of catch rates. In addition, total annual CPUE comparisons were tested

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between years using the same analyses. Data collected from electrofishing effort was not analyzed separately due to a limited amount of information to analyze. Length-Frequency Length-frequency distributions were determined for humpback chub and roundtail chub through the period of the study. Growth Mean annual growth rates were determined from one year of growth on recaptured humpback chub and roundtail chub from 1992–2000 and compared with respect to the length-frequency distributions determined each year of the study. Mean annual growth rates were also estimated and compared among annual recaptured individuals from 1999 and 2000, and all recaptured individuals from 1992-2000. Movement Movement of individuals was also described within Westwater Canyon and between Westwater Canyon and Black Rocks (Chuck McAda, USFWS, Grand Junction, Colorado personal communication). Comparison with ISMP Interagency standardized monitoring program (ISMP) protocol was followed within one pass during each year of this study to allow comparison with historic humpback chub and roundtail chub CPUE information. CPUE was compared between years (1988–2000) using the Kruskal-Wallis nonparametric ANOVA with Dunn’s multiple comparisons test to examine the equality of samples and the two-sample Kolmogorov-Smirnov to compare the distribution of catch rates.

RESULTS Humpback Chub Population Estimates The model selection function of Program CAPTURE resulted in variability among years in determination of the most appropriate estimator for the humpback chub capture-recapture data (Appendix I). The null estimator (Mo) ranked highest in 1998 and 2000 (1.00 and 0.74, respectively). There was no appropriate estimator for the data from 1999. In that year, the highest ranking of the estimator routinely used to calculate population estimates in this study was 0.36 (Chao Mth). Considering the results of the model selection function, the lack of any real justification to consider another estimator (i.e., changes in the probability of capturing an individual due to behavior, flow, etc.), and the outcome of consultation with Dr. Ron Ryel (Utah State University,

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Logan, Utah), the null estimator (Mo) was used to determine the population estimates of adult humpback chub in Westwater Canyon, 1998–2000. The adult humpback chub population estimate was 4,744 individuals in 1998 (Table 1). The profile likelihood interval around this estimate was 3,760 – 14,665 (CV = 0.23; p-hat = 0.035). In 1999, the adult humpback chub population estimate decreased to 2,215 individuals (Table 1). The profile likelihood interval around this estimate was 1,608 – 7,508 (CV = 0.28) with a slightly higher probability of capture (p-hat = 0.041). The adult humpback chub population estimate in 2000 remained approximately the same at 2,201 individuals (Table 1). The probability of capture also remained the same (p-hat = 0.041). However, the profile likelihood interval was tighter (1,335 – 4,124; CV = 0.28). The relationship among these three estimates indicates a short-term decreasing trend in the Westwater Canyon adult humpback chub population (Figure 1). However, the slope of this short-term trend does not significantly depart from zero and each point estimate exceeded the minimum viable population identified in the recovery goals (USFWS 2002). CPUE Total trammel net captures for humpback chub were 501 in 1998, 278 in 1999, and 277 in 2000 (Table 2). Total captures in 1998 included 486 adults, 12 of which were recaptured. An additional three subadult humpback chub were captured in trammel nets. In 1999, 267 adults were included in the total captures. Eight of these individuals were recaptured. Subadult captures in the trammel nets were once again three individuals. The total captures for 2000 included 261 adult humpback chub. Eleven of these were recaptured. Subadult captures included in total trammel net captures for 2000 were slightly increased at five individuals. Mean catch per unit effort (CPUE) decreased across all passes from 1998 to 2000 (Figure 2). The slope of this decreasing trend significantly departs from zero (p < 0.05). The Kruskal-Wallis test indicated there were no significant differences between passes within years, but there were significant differences (p < 0.05) between passes among years. The Kolmogorov-Smirnov test indicated there were no significant differences in the distribution of catch rates between passes within 1998 and 1999. However, there were significant differences (p < 0.05) between passes within 2000 and among years. Comparisons of mean CPUE and the distribution of catch rates between years (all passes combined) indicated significant differences (p < 0.05) between all years. Length-Frequency The length-frequency histograms for Westwater Canyon humpback chub indicated similar bimodal distributions for 1998 and 1999, with a majority of fish in the 240–280 mm and 310–350 mm size classes (Figure 3). In 2000, this distribution became trimodal, with the size classes being 230–260 mm, 280–310 mm, and 340–360 mm. The largest humpback chub caught in each year was 380 mm in 1998, 390 mm in 1999, and 410 mm in 2000 (Figure 3).

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Growth Mean annual growth rates of Westwater Canyon humpback chub (1992-2000) were compared with respect to the bimodal and trimodal distributions of size classes determined from the length-frequency histograms. Mean annual growth rates were 10.58 ± 1.92 mm for humpback chub less than 285 mm and 5.84 ± 1.87 mm for humpback chub greater than 285 mm. Humpback chub mean annual growth was 10.15 ± 2.94 mm for individuals less than 260 mm, 7.70 ± 1.90 mm for individuals between 260 mm and 320 mm, and 6.14 ± 3.11 mm for individuals greater than 320. Analysis of the larger data sets from recaptures in 1999 and 2000 indicate a high degree of variability in growth rates within size classes between years relative to growth rates from all recaptured individuals between 1992-2000 (Figure 4). Movement Movement of humpback chub determined from long-term recaptures (individuals tagged in previous years) varied from 1998 to 2000. However, through the entire study, 80% of recaptures exhibited no net movement. There were 37 long-term recaptures of humpback chub in 1998. These individuals had been tagged in the period 1–6 years prior to 1998. Of the 37 recaptures, 17 (45.9%) were recaptured in the same location, 17 had moved from Cougar Bar (RM 121.5) to Miners Cabin (RM 124.1), and three had moved from Hades Bar (RM 120) to Miners Cabin. Only three of these humpback chub had been captured in 1997. One additional humpback chub was tagged in Black Rocks (RM 136) in August 1998 and recaptured at Miners Cabin in October of the same year. In 1999, there were 44 long-term recaptures of humpback chub that had been initially captured in the previous 1–8 years. Of those, 39 (88.6%) were recaptured in the same location, two had moved from Hades Bar to Cougar Bar, one had moved from Cougar Bar to Hades Bar, one had moved from Miners Cabin to Cougar bar, and one was recaptured in October at Miners Cabin that had moved from Black Rocks, where it had been tagged in September 1998. In addition, twenty-six of these 44 long-term recaptures were captured in 1998. The final year (2000) resulted in the recapture of 65 humpback chub that had been previously captured in the preceding 1–8 years. Of these 65 long-term humpback chub recaptures, 60 (93.8%) were recaptured in the same location, three had moved from Hades Bar to Cougar bar, one had moved from Cougar Bar to Hades Bar, and one had moved from Black Rocks since its original capture in 1999. The 65 long-term recaptures in 2000 resulted in 30 individuals that were captured in 1999 and 23 individuals that were captured in 1998. Comparison with ISMP The historic (1988–2000) ISMP catch per unit effort for humpback chub in Westwater Canyon indicates a decreasing trend (Figure 5). The slope of this decreasing trend significantly departs from zero (p < 0.05). Mean catch per unit effort between 1988 and 2000 as per ISMP sampling protocol was significantly different among years (p < 0.05; Kruskal-Wallis). Furthermore, the distribution of catch rates around the mean was significantly different among years (p < 0.05; Kolmogorov-Smirnov). Length-frequency analysis of humpback chub (≥ 150 mm) data collected via ISMP protocol from 1988–2000 indicates frequent shifts in size structure (Figure 6). Humpback chub in Westwater Canyon appear to move through several types of multi-modal size distributions from year to year.

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Roundtail Chub Population Estimates The model selection function of Program CAPTURE resulted in variability among years in determination of the most appropriate estimator for the roundtail chub capture-recapture data (Appendix II). The jackknife estimator (Mh) ranked highest in 1998 and 2000 (0.85 and 0.88, respectively). However, this estimator was inappropriate for the data in 1999 (0.00). The Darroch estimator (Mt) ranked highest in 1999 (1.00). However, this estimator was not appropriate for the data in 1998 or 2000 (0.05 and 0.00, respectively). Considering these results and to allow a better comparison with the population estimate of humpback chub in Westwater Canyon, the null estimator (Mo) was used to determine the population estimates of adult roundtail chub in Westwater Canyon, 1998–2000. The adult roundtail chub population estimate was 5,005 individuals in 1998 (Table 3). The profile likelihood interval around this estimate was 3,586 – 19,781 (CV = 0.30; p-hat = 0.026). In 1999, the adult roundtail chub population estimate decreased to 4,234 individuals (Table 3). The profile likelihood interval around this estimate was 3,349 – 12,917 (CV = 0.23) with a slightly higher probability of capture (p-hat = 0.037). The adult roundtail chub population estimate in 2000 increased to approximately the 1998 abundance at 4,971 individuals (Table 3). The probability of capture also decreased at the same time (p-hat = 0.031), while the profile likelihood interval was slightly tighter (3,824 – 16,641; CV = 0.25). The relationship among these three estimates indicates short-term stability in the Westwater Canyon adult roundtail chub population (Figure 7). CPUE Total trammel net captures for roundtail were 397 in 1998, 481 in 1999, and 521 in 2000 (Table 2). Total captures in 1998 included 389 adults, seven of which were recaptured. One additional subadult roundtail chub was captured in the trammel nets. In 1999, 457 adults were included in the total captures. Twelve of these individuals were recaptured. Subadult captures in the trammel nets increased to twelve individuals. The total captures for 2000 included 458 adult roundtail chub. Ten of these were recaptured. Subadult captures included in total trammel net captures for 2000 were a project high of 53 individuals. Mean catch per unit effort (CPUE) slightly decreased across all passes from 1998 to 2000 (Figure 8). The slope of this decreasing trend does not significantly depart from zero. Contrary to this decreasing trend, CPUE appeared to increase among passes within years. The Kruskal-Wallis test supported this observation indicating significant differences (p < 0.05) between passes within and among years, except for 2000. The Kolmogorov-Smirnov test indicated there were significant differences (p < 0.05) in the distribution of catch rates between passes within and among all years. Comparisons of mean CPUE and the distribution of catch rates between years (all passes combined) indicated significant differences (p < 0.05) between all years except for mean CPUE between 1999 and 2000.

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Length-Frequency The length-frequency histograms for Westwater Canyon roundtail chub indicated no clear separation of size classes for 1998 and 1999 (Figure 9). In 2000, there was a bimodal distribution with the size classes being 170–190 mm and 240–350 mm. The largest roundtail chub caught in each year was 390 mm in 1998, 380 mm in 1999, and 390 mm in 2000 (Figure 9). Growth Mean annual growth rates of Westwater Canyon roundtail chub were compared with respect to the bimodal distribution of size classes determined from the 2000 length-frequency histogram. To allow comparison between roundtail chub and humpback chub, mean annual growth rates were also examined with respect to the bimodal distribution of humpback chub exhibited in the 1998 and 1999 length-frequency analyses (Figure 3). Mean annual growth rates were 45.67 ± 8.51 mm for roundtail chub less than 210 mm and 16.10 ± 1.70 mm for roundtail chub greater than 210 mm. Roundtail chub less than 285 mm had a mean annual growth rate of 22.56 ± 2.26 mm and roundtail chub greater than 285 mm had a mean annual growth rates of 7.30 ± 1.60 mm. Analysis of the larger data sets from recaptures in 1999 and 2000 indicate a pattern of growth that may shift slightly between years (Figure 10). Movement Movement of roundtail chub as determined from long-term recaptures (individuals tagged in previous years) varied from 1998 to 2000. However, through the entire study, 89% exhibited no net movement. There were 29 long-term recaptures of roundtail chub in 1998. These individuals had been tagged in the period 1–6 years prior to 1998. Of the 29 recaptures, 24 (82.8%) were recaptured in the same location, three had moved from Hades Bar to Cougar Bar, and two had moved from Miners Cabin to Cougar Bar. Only three of these roundtail chub had been captured in 1997. In 1999, there were 34 long-term recaptures of roundtail chub that had been initially captured in the previous 1–7 years. Of those, 33 (97.0%) were recaptured in the same location and one individual had moved from Hades Bar to Cougar Bar. In addition, twenty-two of these 34 long-term recaptures were captured in 1998. Two additional fish were tagged in Black Rocks in September 1999 and subsequently recaptured at Miners Cabin in October 1999. The final year (2000) resulted in the recapture of 46 roundtail chub that had been previously captured in the preceding 1–8 years. Of these 46 long-term roundtail chub recaptures, 41 (87.2%) were recaptured in the same location, two had moved from Hades Bar to Cougar bar, one had moved from Cougar Bar to Miners Cabin, and one had moved from Black Rocks to Miners Cabin (originally tagged in 1999). The 46 long-term recaptures in 2000 resulted in 27 individuals that were captured in 1999 and 13 individuals that were captured in 1998. Comparison with ISMP The historic (1988–2000) ISMP catch per unit effort for roundtail chub in Westwater Canyon indicates a slight decreasing trend (Figure 11). The slope of this trend does not significantly depart from zero. Mean catch per unit effort between 1988 and 2000 as per ISMP sampling protocol was significantly different between 1990 and 2000 and between 1993 and 2000 (p < 0.05; Kruskal-

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Wallis). The distribution of catch rates around the mean was significantly different among years (p < 0.05; Kolmogorov-Smirnov). Length-frequency analysis of roundtail chub (≥ 150 mm) data collected via ISMP protocol from 1988–2000 indicates frequent shifts in size structure (Figure 12). Roundtail chub in Westwater Canyon appear to predominantly move between single mode and bimodal size distributions.

DISCUSSION Population Estimates Population estimates of humpback chub in Westwater Canyon demonstrated a downward trend from 1998 to 2000. This trend is consistent with the point estimates (1998–2000) of humpback chub in Black Rocks (McAda 2003). Previous population estimates (Chart and Lentsch 1999; Nesler 2000), while not as robust, indicate that the humpback chub population in Westwater Canyon is highly variable. Chart and Lentsch (1999) determined the population to be 5,621 individuals in 1994, 10,148 individuals in 1995, and 5,186 individuals in 1996. Nesler determined the Westwater Canyon humpback chub population to be anywhere from 5,719 in 1993 (90% survival) to 1,164 in 1997 (59% survival). Point estimates in Westwater Canyon for 1999 and 2000 may be indicative of a leveling off prior to a rebound in the humpback chub population, or the declining trend could continue. The Westwater Canyon roundtail chub population appeared to be relatively stable from 1998 to 2000. Chart and Lentsch (1999) indicated that the roundtail chub population was declining in the period from 1993 to 1996 (6,809 in 1993, 5,733 in 1994, and 2,551 in 1996). These combined datasets further support the observed variability of chub populations in Westwater Canyon. Identical effort was applied toward the capture of humpback chub and roundtail chub throughout the three years of the study, and, therefore, increases the likelihood that the humpback chub decline is real and not an artifact of sampling bias. This study was not designed to sample for subadult humpback chub in Westwater Canyon for the purpose of generating subadult abundance estimates. Future efforts should include a component of sampling designed to capture subadult humpback chub. This would provide information toward the recovery goal component of determining mean estimated recruitment of humpback chub and also provide additional insight toward population dynamics of the Westwater Canyon population as revealed by the adult population point estimates. Humpback chub and roundtail chub population size patterns observed in this study and by Chart and Lentsch (1999) may indicate that these two species coexist in Westwater Canyon through an equilibrium of population dynamics. While these two studies are not strictly comparable due to different approaches to sampling and analysis of the data, some general observations can be made. From 1993 to 1996, the Westwater Canyon roundtail chub population appeared to be declining. At the same time, the humpback chub population was variable, but relatively higher. Conversely, from 1998 to 2000, adult humpback chub appeared to decline and stabilize while the roundtail chub population was stable and relatively higher. Population estimates of Westwater Canyon humpback chub scheduled for 2003–2005 will contribute to the existing data and further clarify the short-term

9

population trends and population dynamics between humpback chub and roundtail chub in Westwater Canyon. Confidence intervals around humpback chub point estimates became tighter from 1998 to 2000, but there was no considerable improvement in the coefficient of variation or the probability of capture. Tighter confidence intervals in 1999 than in 1998 were an artifact of a smaller population estimate. However, increased trammel net effort in 2000 relative to previous years (1,329 hours in 1998, 1,306 hours in 1999, and 1,951 hours in 2000) resulted in tighter confidence intervals while maintaining a similar point estimate to 1999. Increased effort using alternative sampling methods (e.g., hoop nets and electrofishing) may improve the coefficient of variation and probability of capture for humpback chub and roundtail chub. McAda (2003) demonstrated an improvement in these measures by incorporating a fourth pass to the sampling design. Due to the uncertainty surrounding the model selection function of CAPTURE, it may be necessary to conduct further analyses with this dataset or a combined Black Rocks/Westwater dataset in an attempt to resolve which model is most appropriate. This is especially important given the wide range of estimates generated with the models used (Appendix I and II). Investigation into the utility of Program MARK (White 2002) may result in a more appropriate method of generating future population estimates. Length-Frequency Length frequency analyses for humpback chub and roundtail chub from historic ISMP data and the current study indicate frequent shifts in size distribution. The consistent amount of effort applied toward the current project indicates that the shifts in size distribution in 1998-2000 are probably not due to gear selectivity. However, failure to efficiently capture subadults may contribute to shifts in size distribution within smaller size classes. Shifts in size distribution of adult humpback chub are most probably attributable to annual variations in recruitment and variable growth rates. Growth Growth rates of humpback chub are slower than those of roundtail chub in Westwater Canyon. Growth rates within different size classes of Westwater Canyon humpback chub are variable while those of Black Rocks were not (McAda 2003). Patterns of growth observed in 1998–2000 are similar to those reported by Chart and Lentsch (1999). Chart and Lentsch (1999) reported that humpback chub less than 250 mm grew at approximately twice the rate of those larger than 250 mm. Likewise, humpback chub recaptured in this study less than 285 mm grew at approximately twice the rate of those larger than 285 mm. Roundtail chub also exhibited a similar pattern in growth rates as those reported by Chart and Lentsch (1999). Mean annual growth rate of roundtail chub less than 210 mm in this study and less than 225 mm in the Chart and Lentsch (1999) study was approximately 46 mm. Mean annual growth rate for roundtail chub larger than 210 mm in this study was approximately 16 mm, while Chart and Lentsch (1999) reported 15.6 mm for roundtail chub between 226–250 mm and 12.6 mm for individuals larger than 250 mm. Growth rate and size class differences reported between the two Westwater Canyon studies can be attributed to different conditions (i.e., temperature, water year, food base) that influence these factors.

10

Movement Humpback chub have previously been documented to move less than roundtail chub and other Colorado River fishes (Valdez and Clemmer 1982, Archer et al. 1985, Kaeding et al. 1990, Valdez and Ryel 1995, Chart and Lentsch 2000). Archer et al. (1985) found in Black Rocks that roundtail chub moved more than humpback chub. Valdez and Ryel (1995) later supported that finding by stating that humpback chub moved substantially less than other Colorado River fishes. Valdez and Clemmer (1982) recaptured seven humpback chub in Desolation/Gray canyons that had originally been captured in the same locations. Chart and Lentsch (2000) further supported this finding by reporting the recapture of nine chub at the original capture locations in Desolation/Gray canyons. In Westwater Canyon, little movement of humpback chub and roundtail chub has been documented in the past, but the limited data indicates humpback chub move more than roundtail chub (Chart and Lentsch 1999). A substantially larger dataset of recaptured humpback chub and roundtail chub from this study indicates similar levels of movement: 20% of humpback chub were recaptured in a different location; 11% of roundtail chub were recaptured in a different location. However, from 1998 to 2000, there was a substantially higher rate of movement by humpback chub among all three sites. All roundtail chub movements from 1998 to 2000 were between Cougar Bar and one of the other two sites, while, in addition, Chart and Lentsch (1999) observed limited movement from Miners Cabin to Hades Bar. As long-term recaptures increased in 1999 and 2000 with a smaller period of time between capture occasions for an individual, there was less evidence of movement in recaptured individuals. In 1998, the number of recaptured individuals from 1997 was relatively low. Long-term recaptures were more representative of humpback chub that had been captured from 1992 to 1996, and these individuals exhibited more movement among sites within Westwater Canyon. Thus, short-term site fidelity is supported by the data. However, once humpback chub move to a new location, short-term site fidelity may be re-established for that area. A radiotelemetry component added to future population estimates may provide insight to within and among site movements of humpback chub in Westwater Canyon. Movement of humpback chub and roundtail chub between Black Rocks and Westwater Canyon has been previously documented (Chart and Lentsch 1999; McAda 2003). The capture of three humpback chub and three roundtail chub from 1998 to 2000 in Westwater Canyon that were originally tagged in Black Rocks supports the theory of continued exchange between these two areas. Furthermore, McAda (2003) documented 14 humpback chub that had originally been tagged in Westwater Canyon prior to 1998 that were recaptured in Black Rocks from 1998 to 2000. This migration of approximately 10.5 miles between Black Rocks and Westwater Canyon violates the assumption of closure associated with the models being used for population estimates. The frequency of movement between the two canyon areas is similar to that between areas within Westwater Canyon and exceeds the one migrant per generation required to prevent genetic differentiation (Mills and Allendorf 1996). It may be more appropriate to consider Black Rocks/Westwater Canyon humpback chub a single population and analyze it as such.

11

Comparison with ISMP The decreasing trend of historic CPUE was statistically significant across all years for Westwater Canyon humpback chub. In addition, the difference in mean CPUE was statistically significant between all years except for 1999 and 2000. The adult population point estimates indicated a decreasing trend for 1998-2000. However, the point estimates for 1999 and 2000 were similar. McAda (2002) statee that the marked decline in mean CPUE suggests the Black Rocks humpback chub population has declined since 1986. This statement was further supported by a decrease in CPUE in 2000 and a reflected decrease in the adult population point estimate. Thus, based upon an extremely limited dataset, it appears that CPUE may be indicative of trends in the adult humpback chub population. Additional information from future sampling efforts in Westwater and Black Rocks canyons will aid in further refining the relationship between CPUE and adult population point estimates.

12

CONCLUSIONS • The adult population point estimates of humpback chub in Westwater Canyon indicated a

downward trend from 1998 to 2000, though not statistically significant. • The adult population point estimates of roundtail chub in Westwater Canyon indicated a stable

trend between 1998 and 2000. • Increased trammel net effort (CPUE) resulted in tighter confidence intervals but no real

improvement in probability of capture (p-hat) or coefficient of variation (CV). • Growth rates of humpback chub are lower than those for roundtail chub in Westwater Canyon. • Humpback chub and roundtail chub move between Black Rocks and Westwater Canyon

consistently enough to consider that these two areas contain a single population for each species.

13

RECOMMENDATIONS • Increase trammel net effort (CPUE) in Westwater Canyon. • Use hoop nets and electrofishing to improve probability of capture (p-hat) and coefficient of

variation (CV). • Use smaller mesh trammel nets, hoop nets, minnow traps and electrofishing to target subadult

humpback chub in Westwater Canyon. • Incorporate a fourth pass and additional sampling locations (i.e., upper Cougar, Big Hole) to

improve (p-hat) and coefficient of variation (CV). • Consider Black Rocks and Westwater Canyon a single population and determine a single point

estimate for each year to be consistent with the assumptions for closed population estimates. • Investigate use of most appropriate statistical programs and associated models to generate

future adult humpback chub population estimates. • Include a radiotelemetry component in future adult humpback chub population estimates to

provide additional resolution of movement and site fidelity within and among sampling areas of Westwater Canyon.

14

LITERATURE CITED Archer, D.L., L.R. Kaeding, B.D. Burdick, and C.W. McAda. 1985. A study of the endangered

fishes of the Upper Colorado River. U.S. Fish and Wildlife Service, Grand Junction, Colorado. Chart, T.E., and L. Lentsch. 1999. Flow effects on humpback chub (Gila cypha) in Westwater

Canyon. Utah Division of Wildlife Resources, Salt Lake City, Utah. Publication Number 99–36.

Chart, T.E., and L. Lentsch. 2000. Reproduction and recruitment of Gila spp. and Colorado

pikeminnow (Ptychocheilus lucius) in the Middle Green River 1992–1996. Utah Division of Wildlife Resources, Salt Lake City, Utah. Publication Number 00–18.

Douglas, M.E., R.R. Miller, and W.L. Minckley. 1998. Multivariate discrimination of Colorado

plateau Gila spp.: the “art of seeing well” revisited. Transactions of the American Fisheries Society 127:163-173.

Herbert, L.R., J.R. Tibbetts, D.W. Wilberg, and D.V. Allen. 1999. Water Resources Data; Utah;

Water Year 1998. Water-Data Report UT-98-1. U.S. Department of the Interior, U.S. Geological Survey, Salt Lake City, Utah.

Herbert, L.R., D.V. Allen, D.W. Wilberg, and J.R. Tibbetts. 2000. Water Resources Data; Utah;


Herbert, L.R., D.W. Wilberg, J.R. Tibbetts, and D.V. Allen. 2001. Water Resources Data; Utah;


Herbert, L.R., D.W. Wilberg, and J.R. Tibbetts. 2002. Water Resources Data; Utah; Water Year

2001. Water-Data Report UT-01-1. U.S. Department of the Interior, U.S. Geological Survey, Salt Lake City, Utah.

Kaeding, L.R., B.D. Burdick, P.A. Schrader, and C.W. McAda. 1990. Temporal and spatial relations

between the spawning of humpback chub and roundtail chub in the Upper Colorado River. Transactions of the American Fisheries Society 119:135-144.

McAda, C.W. 2002. Population size and structure of humpback chub in Black Rocks, 1998–2000.

U.S. Fish and Wildlife Service, Colorado River Fisheries Project Office, Grand Junction, Colorado.

Miller, R.R. 1946. Gila cypha, a remarkable new species of cyprinid fish from the Colorado River in

Grand Canyon, Arizona. Journal of the Washington Academy of Sciences 36:409–415. Mills, L.S., and F.W. Allendorf. 1996. The one-migrant-per-generation rule in conservation and

management. Conservation Biology 10:1509-1518.

15

Nesler, T.P. 2000. Recovery of the Colorado River endangered fishes: biological recovery goals and criteria for Colorado pikeminnow, humpback chub, razorback sucker, and bonytail. Colorado Division of Wildlife, Fort Collins, Colorado.

Otis, D.L., K.P. Burnham, G.C. White, and D.R. Anderson. 1978. Statistical inference from capture

data on closed animal populations. Wildlife Monographs. 62:1–135. Rexstad, E. and K. Burnham. 1991. User’s guide for interactive program CAPTURE. Unpublished

report, Colorado Cooperative Fish and Wildlife Research Unit, Colorado State University, Fort Collins, Colorado.

USFWS. 1987. Interagency Standardized Monitoring Program Handbook. U.S. Fish and Wildlife

Service, Colorado River Fisheries Project Office, Grand Junction, Colorado. USFWS. 1990. Humpback chub recovery plan, 2nd revision. Report of Colorado River Fishes

Recovery Team to U.S. Fish and Wildlife Service, Region 6, Denver, Colorado. USFWS. 2002. Humpback chub (Gila cypha) recovery goals: an amendment and supplement to the

humpback chub recovery plan. U.S. Fish and Wildlife Service, Mountain-Prairie Region 6, Denver, Colorado.

Valdez, R.A., and G.C. Clemmer. 1982. Life history and prospects for recovery of humpback chub

and bonytail chub. Pages 109–110 in W.H. Miller, H.M. Tyus, and C.A. Carlson, eds., Fishes of the Upper Colorado River system: present and future. Western Division, American Fisheries Society, Bethesda, MD.

Valdez, R.A., and R.J. Ryel. 1995. Life history and ecology of the humpback chub (Gila cypha)in

the Colorado River, Grand Canyon, Arizona. Final Report to the Bureau of Reclamation, Salt Lake City, Utah. Contract No. 0-CS-40-09110. BIO/WEST Report No. TR-250-08.

Valdez, R.A., P. Mangan, R. Smith, and B. Nilson. 1982. Part 2 Colorado River Fishery Project

Final Report Field Investigations. U.S. Fish and Wildlife Service and U.S. Bureau of Reclamation, Salt Lake City, Utah.

White, G.C., D.R. Anderson, K.P. Burnham, and D.L. Otis. 1982. Capture-recapture and removal

methods for sampling closed populations. Los Alamos National Laboratory, LA-8787-NERP, Los Alamos, New Mexico.

16

Table 1. Population estimate (N) for humpback chub adults (>200 mm) in Westwater Canyon 1998–2000. Population estimate generated using the null estimator (Mo) within program CAPTURE. The profile likelihood interval, coefficient of variation (CV), and probability of capture (p-hat) are included with the respective population estimates.

Year N Profile Likelihood Interval

CV p-hat

1998 4,744 3,760–14,665 0.23 0.035

1999 2,215 1,608–7,508 0.28 0.041

2000 2,201 1,335–4,124 0.28 0.041

Table 2. Total humpback chub captures in Westwater Canyon 1998–2000. Includes number of adult

captures, adult recaptures, and subadults caught.

Year Total Captures

Adult Captures

Adult Recaptures

Subadult Captures

1998 501 486 12 3

1999 278 267 8 3

2000 277 261 11 5

17

Table 3. Population estimate (N) for roundtail chub adults (>200 mm) in Westwater Canyon 1998–2000. Population estimate generated using the null estimator (Mo) within program CAPTURE. The profile likelihood interval, coefficient of variation (CV), and probability of capture (p-hat) are included with the respective population estimates.

Year N Profile Likelihood Interval

CV p-hat

1998 5,005 3,586–19,781 0.30 0.026

1999 4,234 3,349–12,917 0.23 0.037

2000 4,971 3,824–16,641 0.25 0.031

Table 4. Total roundtail chub captures in Westwater Canyon 1998–2000. Includes number of adult

captures, adult recaptures, and subadults caught.

Year Total Captures

Adult Captures

Adult Recaptures

Subadult Captures

1998 397 389 7 1

1999 481 457 12 12

2000 521 458 10 53

18

Westwater Canyon Humpback Chub Adult Population Estimate 1998-2000

0

2000

4000

6000

8000

10000

12000

14000

16000

1998 1999 2000

Year

Np>0.05

Figure 1. Westwater Canyon adult humpback chub population estimates (N) for 1998–2000. Each

point estimate includes respective profile likelihood confidence intervals. Line represents short-term trend among the three point estimates. The p-value indicates statistical significance of the trend line.

Westwater Canyon Humpback Chub CPUE 1998-2000

0

0.1

0.2

0.3

0.4

0.5

0.6

1998A 1998B 1998C 1999A 1999B 1999C 2000A 2000B 2000C

Year

CPU

E (f

ish/

tram

mel

net

hou

r)

p<0.05

Figure 2. Westwater Canyon humpback chub trammel net catch per unit effort by pass for 1998–

2000. CPUE for each pass includes respective standard error. Line represents trend among all passes in all years. The p-value indicates statistical significance of the trend line.

19

Westwater Canyon Humpback Chub Length-Frequency Distribution 1998

n=489

0

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30

40

50

70 90 110

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Freq

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)

Westwater Canyon Humpback Chub Length-Frequency Distribution

1999n=270

0

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Westwater Canyon Humpback Chub Length-Frequency Distribution

2000n=266

0

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Freq

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)

Figure 3. Westwater Canyon humpback chub length-frequency histograms for 1998–2000. Frequency is illustrated as number of total individuals within a given size class.

20

Westwater Canyon Humpback Chub Annual Incremental Growth

05

10152025303540

180-200 201-220 221-240 241-260 261-280 281-300 301-320 321-340 341-360

Initial Size (mm)

Mea

n A

nnua

l Gro

wth

(mm

)

1998-1999 1999-2000 All Years

Figure 4. Westwater Canyon humpback chub annual incremental growth for individuals between

1998–1999 and 1999–2000, and among all years (1992–2000). All years data includes estimates of average annual growth for individuals that were recaptured after more than one year at large. Standard error is not included for respective size classes and years that annual incremental growth was determined from one individual.

Westwater Canyon Humpback Chub Historic ISMP CPUE

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

CPU

E (f

ish/

tram

mel

net

hou

r)

p<0.05

Figure 5. Westwater Canyon humpback chub catch per unit effort for samples collected using

ISMP protocol from 1988 to 2000. CPUE for each year includes respective standard error. Line represents trend among all passes in all years. The p-value indicates statistical significance of the trend line.

21

Humpback Chub ISMP Length-Frequency1988

0

5

10

15

20

Length (m m )


0

5

10

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Length (m m )

Humpback Chub ISMP Length-Frequency

1989

0

5

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Length (m m )


0

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20

Length (m m )


1990

0

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1991

0

5

10

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Length (m m )


0

5

10

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20

Length (m m )

Figure 6. Westwater Canyon humpback chub ISMP length-frequency histograms for 1988–2000.

Frequency is illustrated as percentage of total individuals (n) within a given size class.

22


0

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Length (m m )


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1997

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0

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1998

0

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Figure 6 (continued). Westwater Canyon humpback chub ISMP length-frequency histograms for

1988–2000. Frequency is illustrated as percentage of total individuals (n) within a given size class.

23

Westwater Canyon Adult Roundtail Chub Population Estimate 1998-2000

0

5000

10000

15000

20000

25000

1998 1999 2000

Year

N

p>0.05

Figure 7. Westwater Canyon adult roundtail chub population estimates (N) for 1998–2000. Each

point estimate includes respective profile likelihood confidence intervals. Line represents short-term trend among the three point estimates. The p-value indicates statistical significance of the trend line.

Westwater Canyon Roundtail Chub CPUE 1998-2000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1998A 1998B 1998C 1999A 1999B 1999C 2000A 2000B 2000C

Year

CPU

E (f

ish/

tram

mel

net

hou

r)

p>0.05

Figure 8. Westwater Canyon roundtail chub trammel net catch per unit effort by pass for 1998–

2000. CPUE for each pass includes respective standard error. Line represents trend among all passes in all years. The p-value indicates statistical significance of the trend line.

24

Westwater Canyon Roundtail Chub Length-Frequency Distribution 1998n=390

01020304050607080

70 90 110

130

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Westwater Canyon Roundtail Chub Length-Frequency Distribution 1999

n=469

01020304050607080

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Westwater Canyon Roundtail Chub Length-Frequency Distribution 2000

n=511

01020304050607080

70 90 110

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190

210

230

250

270

290

310

330

350

370

390

410

430

450

Length (mm)

Freq

uenc

y (n

)

Figure 9. Westwater Canyon roundtail chub length-frequency histograms for 1998–2000.

Frequency is illustrated as number of total individuals within a given size class.

25

Westwater Canyon Roundtail Chub Annual Incremental Growth

05

10152025303540

180-200 201-220 221-240 241-260 261-280 281-300 301-320 321-340 341-360

Initial Size (mm)

Mea

n A

nnua

l Gro

wth

(mm

)

1998-1999 1999-2000 All Years

Figure 10. Westwater Canyon roundtail chub annual incremental growth for individuals between

1998–1999 and 1999–2000, and among all years (1992–2000). All years data includes estimates of average annual growth for individuals that were recaptured after more than one year at large. Standard error is not included for respective size classes and years that annual incremental growth was determined from one individual.

Westwater Canyon Roundtail Chub Historic ISMP CPUE

0

0.1

0.20.3

0.4

0.5

0.60.7

0.8

0.9

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

CPU

E (f

ish/

tram

mel

net

hou

r)

p>0.05

Figure 11. Westwater Canyon roundtail chub catch per unit effort for samples collected using ISMP

protocol from 1988 to 2000. CPUE for each year includes respective standard error. Line represents trend among all passes in all years. The p-value indicates statistical significance of the trend line.

26

Roundtail Chub ISMP Length-Frequency1988

0

5

10

15

20

Length (m m )


0

5

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20

Length (m m )

Roundtail Chub ISMP Length-Frequency

1989

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0

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1990

0

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1991

0

5

10

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20

Length (m m )


0

5

10

15

20

Length (m m )

Figure 12. Westwater Canyon roundtail chub ISMP length-frequency histograms for 1988–2000.

Frequency is illustrated as percentage of total individuals (n) within a given size class.

27


0

5

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20

Length (m m )


0

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Length (m m )


1997

0

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0

5

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Length (m m )


1998

0

5

10

15

20

Length (m m )

Figure 12 (continued). Westwater Canyon roundtail chub ISMP length-frequency histograms for

1988–2000. Frequency is illustrated as percentage of total individuals (n) within a given size class.

28

Appendix I. Summary of population estimates generated within Program CAPTURE for adult humpback chub in Westwater Canyon, 1998–2000. Information for comparison within each year of the study among the six estimators used includes the population estimate (N), 95% confidence intervals, coefficient of variation (CV), probability of capture (p-hat), and the model selection criteria.

Year Estimator N Confidence Interval*

CV p-hat Model Selection Criteria

Mo 4,744 3,085–7,462 (3,760–14,665 ) 0.23 0.035 1.00

Jackknife Mh 958 902–1,022 0.03 0.173 0.84

Darroch Mt 3,190 2,427–4,251 (2,860–24,710) 0.14 0.050 0.00

Chao Mth 6,723 3,972–11,647 0.28 0.023 0.46

Chao Mt 6,243 3,770–10,579 0.27 0.030 -

1998

Chao Mh 9,848 5,722–17,224 0.29 0.017 -

Mo 2,215 1,322–3,863 (1,608–7,508) 0.28 0.041 0.24

Jackknife Mh 525 484–573 0.04 0.175 0.15

Darroch Mt 2,670 1,551–4,766 (1,673–6,613) 0.30 0.033 0.00

Chao Mth 3,059 1,637–5,961 0.34 0.030 0.36

Chao Mt 2,699 1,502–5,057 0.32 0.033 -

1999

Chao Mh 4,460 2,326–8,803 0.35 0.021 -

Mo 2,201 1,308–3,855 (1,335–4,124) 0.28 0.041 0.74

Jackknife Mh 509 469–556 0.04 0.178 0.74

Darroch Mt 1,713 1,116–2,728 (1,218–3,978) 0.23 0.053 0.60

Chao Mth 2,216 1,276–4,028 0.30 0.040 0.62

Chao Mt 1,862 1,134–3,199 0.27 0.047 -

2000

Chao Mh 3,102 1,781–5,571 0.30 0.029 -

*95% confidence intervals are provided for all estimators. Profile likelihood intervals are provided in parentheses for Mo and the Darroch Mt.

29

Appendix II. Summary of population estimates generated within Program CAPTURE for adult roundtail chub in Westwater Canyon, 1998–2000. Information for comparison within each year of the study among the six estimators used includes the population estimate (N), 95% confidence intervals, coefficient of variation (CV), probability of capture (p-hat), and the model selection criteria.

Year Estimator N Confidence Interval*

CV p-hat Model Selection Criteria

Mo 5,005 2,869–8,980 (3,586–19,781) 0.30 0.026 0.76

Jackknife Mh 770 720–827 0.04 0.171 0.85

Darroch Mt 2,553 1,824–3,651 (2,180–27,386) 0.18 0.053 0.05

Chao Mth 9,179 4,532–19,041 0.38 0.013 0.29

Chao Mt 5,121 2,738–9,922 0.34 0.023 -

1998

Chao Mh 10,812 5,360–22,246 0.38 0.012 -

Mo 4,234 2,754–6,665 (3,349–12,917) 0.23 0.037 0.13

Jackknife Mh 900 846–962 0.03 0.174 0.00

Darroch Mt 2,999 2,231–4100 (2,622–16,739) 0.16 0.050 1.00

Chao Mth 6,206 3,599–10,978 0.29 0.027 0.66

Chao Mt 5,129 3,115–8,673 0.27 0.030 -

1999

Chao Mh 8,708 5,064–15,235 0.29 0.018 -

Mo 4,971 3,107–8,144 (3,824–16,641) 0.25 0.031 0.78

Jackknife Mh 904 850–966 0.03 0.173 0.88

Darroch Mt 5,038 3,266–7,929 (3,718–14,667) 0.23 0.033 0.00

Chao Mth 7,458 4,123–13,830 0.31 0.020 0.27

Chao Mt 6,116 3,544–10,831 0.29 0.027 -

2000

Chao Mh 10,493 5,800–19,309 0.32 0.015 -

*95% confidence intervals are provided for all estimators. Profile likelihood intervals are provided in parentheses for Mo and the Darroch Mt.

30

Appendix III. Colorado River Water Data 1998-2000 Environmental conditions of the Colorado River in Westwater Canyon for 1998-2000 are presented in the following tables and figures. Mean daily discharge (cfs), mean daily temperature (oC) and suspended sediment (mg/l) were recorded at USGS gage #09163500 (Colorado River near Colorado-Utah State Line; above Westwater Canyon). In the absence of that data daily instantaneous temperature (oC) values and suspended sediment (mg/l) data are reported as recorded at USGS gage #09180500 (Colorado River near Cisco; below Westwater Canyon). Additional environmental parameters for the period of record as recorded at both gages are reported in Herbert et al. (1999, 2000, 2001, 2002). Appendix III Table 1. Mean daily discharge (cfs) of Colorado River near Colorado-Utah state line

(USGS gage #09163500) for Fall 1998. Westwater Canyon humpback chub sampling dates are in bold.

Date Discharge Date Discharge

9/1/1998 3660 10/1/1998 4120 9/2/1998 3820 10/2/1998 4210 9/3/1998 4020 10/3/1998 4540 9/4/1998 3990 10/4/1998 4680 9/5/1998 3800 10/5/1998 5060 9/6/1998 3720 10/6/1998 5180 9/7/1998 3760 10/7/1998 5090 9/8/1998 3670 10/8/1998 4920 9/9/1998 3600 10/9/1998 4760

9/10/1998 3550 10/10/1998 4780 9/11/1998 3670 10/11/1998 4740 9/12/1998 4310 10/12/1998 4670 9/13/1998 5500 10/13/1998 4640 9/14/1998 5200 10/14/1998 4590 9/15/1998 5090 10/15/1998 4560 9/16/1998 4930 10/16/1998 4470 9/17/1998 4880 10/17/1998 4620 9/18/1998 4800 10/18/1998 4660 9/19/1998 4710 10/19/1998 4750 9/20/1998 4550 10/20/1998 4730 9/21/1998 4430 10/21/1998 4700 9/22/1998 4360 10/22/1998 4770 9/23/1998 4400 10/23/1998 4860 9/24/1998 4450 10/24/1998 4970 9/25/1998 4260 10/25/1998 4840 9/26/1998 4190 10/26/1998 5350 9/27/1998 4080 10/27/1998 5500 9/28/1998 4020 10/28/1998 5920 9/29/1998 3990 10/29/1998 5740 9/30/1998 4040 10/30/1998 5360

-- -- 10/31/1998 5400

31

Appendix III Table 2. Daily instantaneous temperature (oC) values (September) of Colorado River near Cisco (USGS gage #09180500) and mean daily temperature (oC) of Colorado River near Colorado-Utah State line (USGS gage #09163500) for Fall 1998. Westwater Canyon humpback chub sampling dates are in bold.

Date Temperature Date Temperature

9/1/1998 23.0 10/1/1998 17.3 9/2/1998 23.0 10/2/1998 15.8 9/3/1998 23.0 10/3/1998 15.6 9/4/1998 23.0 10/4/1998 13.8 9/5/1998 22.0 10/5/1998 12.6 9/6/1998 22.0 10/6/1998 11.6 9/7/1998 22.0 10/7/1998 11.8 9/8/1998 22.0 10/8/1998 12.2 9/9/1998 22.0 10/9/1998 12.8

9/10/1998 22.0 10/10/1998 13.0 9/11/1998 22.0 10/11/1998 12.9 9/12/1998 22.0 10/12/1998 12.8 9/13/1998 21.0 10/13/1998 12.6 9/14/1998 21.0 10/14/1998 12.7 9/15/1998 21.0 10/15/1998 12.9 9/16/1998 21.0 10/16/1998 12.5 9/17/1998 20.0 10/17/1998 11.8 9/18/1998 20.0 10/18/1998 11.2 9/19/1998 20.0 10/19/1998 10.8 9/20/1998 18.0 10/20/1998 10.9 9/21/1998 18.0 10/21/1998 11.0 9/22/1998 18.0 10/22/1998 11.3 9/23/1998 18.0 10/23/1998 12.0 9/24/1998 18.0 10/24/1998 12.0 9/25/1998 18.0 10/25/1998 11.6 9/26/1998 18.0 10/26/1998 11.4 9/27/1998 18.0 10/27/1998 11.4 9/28/1998 18.0 10/28/1998 11.0 9/29/1998 18.0 10/29/1998 10.2 9/30/1998 18.0 10/30/1998 9.8

-- -- 10/31/1998 9.8

Appendix III Table 3. Suspended sediment (mg/l) of Colorado River near Cisco (USGS gage

#09180500; September) and Colorado River near Colorado-Utah state line (USGS gage #09163500; October) for Fall 1998.

Date Time Suspended

Sediment Date Time Suspended

Sediment 9/23/1998 1135 164 10/8/1998 1115 104 9/23/1998 1136 159 10/8/1998 1200 82

32

Appendix III Table 4. Mean daily discharge (cfs) of Colorado River near Colorado-Utah state line (USGS gage #09163500) for Fall 1999. Westwater Canyon humpback chub sampling dates are in bold.


9/1/1999 5270 10/1/1999 6140 9/2/1999 5730 10/2/1999 6630 9/3/1999 6200 10/3/1999 7260 9/4/1999 6830 10/4/1999 7870 9/5/1999 6780 10/5/1999 8010 9/6/1999 6640 10/6/1999 7300 9/7/1999 6140 10/7/1999 6600 9/8/1999 5800 10/8/1999 6420 9/9/1999 5610 10/9/1999 6280

9/10/1999 5470 10/10/1999 5780 9/11/1999 5390 10/11/1999 5270 9/12/1999 5380 10/12/1999 4930 9/13/1999 5600 10/13/1999 4800 9/14/1999 5400 10/14/1999 4810 9/15/1999 5270 10/15/1999 4660 9/16/1999 5450 10/16/1999 4690 9/17/1999 5730 10/17/1999 4820 9/18/1999 5820 10/18/1999 5050 9/19/1999 5970 10/19/1999 5110 9/20/1999 6580 10/20/1999 5150 9/21/1999 6900 10/21/1999 5130 9/22/1999 6740 10/22/1999 5040 9/23/1999 6440 10/23/1999 5130 9/24/1999 6340 10/24/1999 5120 9/25/1999 6380 10/25/1999 5120 9/26/1999 6540 10/26/1999 5110 9/27/1999 6390 10/27/1999 5100 9/28/1999 6190 10/28/1999 5200 9/29/1999 6110 10/29/1999 5190 9/30/1999 6140 10/30/1999 5150

-- -- 10/31/1999 5280

33

Appendix III Table 5. Mean daily temperature (oC) of Colorado River near Colorado-Utah State line (USGS gage #09163500) for Fall 1999. Westwater Canyon humpback chub sampling dates are in bold.


9/1/1999 20.0 10/1/1999 13.3 9/2/1999 19.0 10/2/1999 13.5 9/3/1999 18.9 10/3/1999 13.8 9/4/1999 18.1 10/4/1999 13.8 9/5/1999 17.8 10/5/1999 13.6 9/6/1999 18.1 10/6/1999 13.8 9/7/1999 18.4 10/7/1999 13.8 9/8/1999 18.7 10/8/1999 13.6 9/9/1999 18.4 10/9/1999 13.7

9/10/1999 18.6 10/10/1999 14.1 9/11/1999 19.3 10/11/1999 14.3 9/12/1999 19.1 10/12/1999 14.2 9/13/1999 18.6 10/13/1999 14.2 9/14/1999 17.8 10/14/1999 13.8 9/15/1999 17.5 10/15/1999 13.3 9/16/1999 17.3 10/16/1999 12.5 9/17/1999 17.9 10/17/1999 10.5 9/18/1999 18.0 10/18/1999 9.7 9/19/1999 17.5 10/19/1999 10.0 9/20/1999 16.4 10/20/1999 9.8 9/21/1999 16.2 10/21/1999 9.9 9/22/1999 15.7 10/22/1999 10.1 9/23/1999 16.0 10/23/1999 10.3 9/24/1999 16.6 10/24/1999 10.1 9/25/1999 17.0 10/25/1999 9.9 9/26/1999 17.0 10/26/1999 9.8 9/27/1999 15.9 10/27/1999 9.8 9/28/1999 14.0 10/28/1999 9.4 9/29/1999 12.7 10/29/1999 9.5 9/30/1999 12.3 10/30/1999 9.0

-- -- 10/31/1999 8.9



Date Time Suspended


Sediment 9/20/1999 1200 1350 10/8/1999 1130 105 9/20/1999 1240 1190 10/8/1999 1200 51

34

Appendix III Table 7. Mean daily discharge (cfs) of Colorado River near Colorado-Utah state line (USGS gage #09163500) for Fall 2000. Westwater Canyon humpback chub sampling dates are in bold.


9/1/2000 4480 10/1/2000 3280 9/2/2000 4210 10/2/2000 3200 9/3/2000 3890 10/3/2000 3090 9/4/2000 3750 10/4/2000 2910 9/5/2000 3740 10/5/2000 2900 9/6/2000 3740 10/6/2000 3140 9/7/2000 3790 10/7/2000 3240 9/8/2000 3870 10/8/2000 3200 9/9/2000 4020 10/9/2000 3160

9/10/2000 3980 10/10/2000 3150 9/11/2000 3930 10/11/2000 3170 9/12/2000 3720 10/12/2000 3340 9/13/2000 3490 10/13/2000 3390 9/14/2000 3290 10/14/2000 3410 9/15/2000 3160 10/15/2000 3420 9/16/2000 3090 10/16/2000 3520 9/17/2000 3030 10/17/2000 3470 9/18/2000 3110 10/18/2000 3480 9/19/2000 3330 10/19/2000 3370 9/20/2000 3300 10/20/2000 3310 9/21/2000 3300 10/21/2000 3230 9/22/2000 3520 10/22/2000 3280 9/23/2000 3710 10/23/2000 3330 9/24/2000 4160 10/24/2000 3620 9/25/2000 3870 10/25/2000 3770 9/26/2000 3830 10/26/2000 3810 9/27/2000 3760 10/27/2000 3760 9/28/2000 3560 10/28/2000 3710 9/29/2000 3250 10/29/2000 3730 9/30/2000 3320 10/30/2000 3770

-- -- 10/31/2000 4040

35

Appendix III Table 8. Mean daily temperature (oC) of Colorado River near Colorado-Utah State line (USGS gage #09163500) for Fall 2000. Westwater Canyon humpback chub sampling dates are in bold.


9/1/2000 20.0 10/1/2000 16.9 9/2/2000 18.6 10/2/2000 16.9 9/3/2000 18.8 10/3/2000 17.0 9/4/2000 19.3 10/4/2000 16.9 9/5/2000 19.5 10/5/2000 16.5 9/6/2000 18.2 10/6/2000 15.5 9/7/2000 18.3 10/7/2000 14.8 9/8/2000 19.1 10/8/2000 14.4 9/9/2000 18.3 10/9/2000 14.4

9/10/2000 18.5 10/10/2000 14.2 9/11/2000 18.3 10/11/2000 13.4 9/12/2000 18.7 10/12/2000 12.9 9/13/2000 19.0 10/13/2000 12.4 9/14/2000 19.2 10/14/2000 12.2 9/15/2000 19.4 10/15/2000 11.8 9/16/2000 19.6 10/16/2000 11.6 9/17/2000 19.2 10/17/2000 11.6 9/18/2000 19.2 10/18/2000 11.5 9/19/2000 19.2 10/19/2000 11.5 9/20/2000 18.8 10/20/2000 11.6 9/21/2000 17.8 10/21/2000 11.5 9/22/2000 17.1 10/22/2000 11.7 9/23/2000 16.3 10/23/2000 11.8 9/24/2000 14.2 10/24/2000 11.5 9/25/2000 13.4 10/25/2000 11.3 9/26/2000 13.4 10/26/2000 10.9 9/27/2000 14.4 10/27/2000 10.9 9/28/2000 15.5 10/28/2000 11.1 9/29/2000 16.4 10/29/2000 10.8 9/30/2000 16.6 10/30/2000 11.0

-- -- 10/31/2000 10.2



Date Time Suspended


Sediment 9/14/2000 1230 94 10/30/2000 1020 63 9/14/2000 1330 99 10/30/2000 1100 69

36

Documents

POPULATION ESTIMATES FOR HUMPBACK CHUB (GILA CYPHA) AND ROUNDTAIL